This section is from the book "The Manufacture Of Liquors, Wines, And Cordials, Without The Aid Of Distillation", by Pierre Lacour. Also available from Amazon: Manufacture of Liquors, Wines, and Cordials, Without the Aid of Distillation.
The sugar, honey, pepper, etc, will be perceptible to the taste, if the liquid be evaporated to dryness, the tannin will be known by the liquid forming a dark line, by the addition of the sesquioxide of iron; the starch will be known by the addition of iodine in solution, and the presence of grain oil will be denoted by nitrate of silver.
Oil in Liquors. - Take of nitrate of silver, ten grains pure water, one ounce; dissolve the nitrate of silver in the water; to half a glass of the liquid supposed to contain grain oil, add twenty-five drops of the solution of nitrate of silver; if there be any grain oil, it will be converted into a black powder, and will be seen floating on the surface of the liquid.
The action of the silver is not always immediate; the glass should be exposed to a strong light, the better to enable the operator to observe any of the powder that might be floating on the surface of the liquid. It has been observed, that the action of the oxide of silver is not immediate; from one to twenty-four hours is sometimes necessary in testing a sample that may have been well rectified, either by distillation or filtration.
Iodine Test for Starch in Liquors. - Iodine, one ounce; alcohol, five ounces; dissolve. To half a glass of spirit, add a few drops of the solution of iodine, if starch is present the product will be purple, and dark purplish spots or specks.
Now it must be obvious, that when the tests mentioned fail in denoting the presence of these articles mentioned, the spirit is unadulterated, as the articles sought for by these tests, viz. sugar, honey, and starch, are those that are used both in America and Europe, by all classes of manufacturers, in adulterating liquors.
Take of the liquid to be examined, one hundred parts, and a solution of subacetate of lead, formed by taking litharge, fifteen parts; acetate of lead, twelve parts; water, two hundred parts: boil for twenty minutes, or until reduced to one half. Take of this twelve parts, agitate together, and strain through muslin; then take potash, that has been brought to red heat in a ladle, and add it in powder to the liquid, as long as it continues to dissolve; the alcohol will be seen floating on top of the mixture. The quantity of spirit can be estimated by means of a graduated tube.
The most certain way to determine the quantity of alcohol contained in a given quantity of any li quid, is to separate it from the non-volatile constituents by distillation. Any kind of small still can be made available for this purpose. Take for the purpose three hundred parts of the liquid to be examined, measured in a glass tube carefully, and slowly distil over one hundred parts, or one third of the liquor in the still, making use of a graduating tube as the recipient of the distilled liquid, and stopping the ope ration when the distilled liquor reaches the hun dredth degree; then obtain the amount of alcoho the distilled liquor contains, by means of the hydro meter, and dividing the result by three, you have the per centage of alcohol that the liquid contains. If for example, the hundred parts of distilled liquor contained thirty parts of alcohol, the liquid submit ted to distillation contains ten per cent, of alcohol but if, from want of attention, there should be dis tilled over more than one hundred parts of the li quor, it will not answer to divide the alcoholic strength of the product by three to obtain the per centage of the alcohol of the liquor submitted to dis tillation. You must employ as a divisor the num ber which expresses the relation of the volume of the distilled product to the bulk of the wine. If for example, you have one hundred and six parts of distilled liquor, containing (by the hydrometer) thir ty-three parts of alcohol, you divide 300 by 106 which gives 2.83, and then divide 33 by 2.83, which gives 11.66; the last number expresses the per cent-age of alcohol of the liquor submitted for examina tion.